I likewise did a direct upgrade from Tiger to Leopard on my 2.4GHz MBP which, at the time also had 2GB Ram (now I have 4... it's just so cheap!)

Anyways, I had zero problems. Everything worked very well... and having just migrated over from the Windows world when I did that, I was needless to say, quite impressed. (I could tell you horror stories about trying a direct upgrade in Windows).

Last month I re-did a clean install of OS X, but only because I swapped out my MBP's Hard Drive for a bigger one. But I definitely gotta say that Apple has really perfected the whole direct upgrade. No app problems, no malfunctions, no errors. Works like a charm.